This invention relates to die-casting methods and apparatus, and more particularly, to methods and apparatus for die-casting V-blocks for internal combustion engines.
Die-casting is being used for the manufacture of larger and larger articles. Such large automotive parts as internal combustion engine blocks and the housings for automatic transmissions are now commonly manufactured with die-casting as the first step in formation of the part. Such parts have extensive and complex surfaces with close tolerances; and die-casting permits their formation in high production, eliminating costly machining operations and saving metal. Die-casting requires extreme pressures exerted on the liquid metal and large amounts of heat are released from the molten metals as they change state. Massive dies are required to maintain dimensional tolerances within the limits making such operations economically attractive and to provide the strength to withstand the stresses resulting from high pressures and forces. The die-casting molds for such large automotive parts as automatic transmission housings are, for example, frequently seven to eight feet (2.1-2.5 meters) tall, seven to eight fee (2.1-2.5 meters) wide, and six to seven feet (1.8-2.1 meters) thick when closed, and must be manufactured from high-grade, high-tensile strength steel. (The words xe2x80x9cmoldxe2x80x9d and xe2x80x9cdiexe2x80x9d are used interchangeably herein.)
Such molds frequently include one stationary element, one movable element operated by the die-casting machine to close the mold, and several slidable elements referred as xe2x80x9cslidesxe2x80x9d that move transversely of the direction of movement of the die-casting machine to provide a mold cavity with intricate and re-entrant surface configurations. The mold slides, which slide transversely of the direction of movement of the die-casting machine, are generally moved by hydraulic cylinders to their proper positions.
Die-casting has become desirable as a manufacturing method for parts such as automobile engine blocks and transmission housings because it can produce intricately shaped parts to close tolerances. Die-casting can provide such parts with strength and intricately shaped surfaces without extensive and expensive machining operations. Such parts have wall thicknesses designed to take advantage of the economy of die-casting operations. Misalignment of the mold parts due, for example, to warping of the mold, misalignment of the mold on the molding machine, or non-parallelism in the molding machine platen surfaces or their direction of the movement, can vary wall thicknesses and distort part surface dimensions to unacceptable limits and result in a substantial waste of die-cast parts.
The die-casting of V-blocks for internal combustion engines poses a difficult problem because the formation of the cylinders of a V-block requires a plurality of cylinder-forming die core elements that must be moved in the die at the acute angle on which the internal combustion engine""s pistons will operate, and because the V-blocks are large and heavy and are subject to close tolerances in their dimensions.
In the die-casting of such engine blocks, a plurality of movable die parts are registered in a die-closed position to form a die cavity, and are subsequently retracted to permit removal of the cast part from the die. These die parts must be held in place in the closed position against extremely high molten metal injection forces, sometimes up to 500,000 to 1,000,000 pounds. The die parts, which are movable in a direction coinciding with the principal or longitudinal direction of movement of the die-casting machine, are locked in place by the closing mechanism of the die-casting machine itself. The die parts, or slides, which move in a direction parallel to the parting plane, which is perpendicular to the axis of movement of the die-casting machine, are locked in place when the die is closed by interacting surfaces on the slides and the die cover and the closing mechanism of the die-casting machine. Even though substantial force builds up during the metal injection step in die-casting, movable die members can be satisfactorily locked in a die-closed position by the forces imposed thereon by the closing mechanism of the die-casting machine when they move only in these two directions. However, the locking of die core elements which are movable at an acute angle with respect to the longitudinal axis of the die-casting machine has presented a different and difficult problem.
Wherever the descriptions herein refer to die core pieces or die core elements, or cylinder-forming die core pieces, the references refer to those die elements that move on an acute angle with respect to the direction of movement of the die-casting machine and can carry and position cylinder-forming sleeves in the V-block casting or can otherwise form the cylinders of the V-block casting.
U.S. Pat. No. 3,433,292 discloses a die in which the die core elements have been locked in die-closed positions by engagement of a back-up plate with the piston rods of the separate hydraulic cylinder means used for moving the die core elements. This locking mechanism has not been satisfactory because the large angular forces imposed on the piston rods by the injection pressure of the molten metal adversely affect the packings of the hydraulic cylinders, and cause rapid wear in the area of contact between the piston ends and the back-up plate because of sliding action and relatively small contact areas.
U.S. Pat. No. 4,206,799 discloses a further development in the die-casting of V-blocks by providing in a die an ejector die assembly comprising, in addition to a plurality of slides, a plurality of die members including die core elements movable relative to the die assembly in a direction at an acute angle to the longitudinal axis of movement of the die-casting machine, and a separate back-up plate means connected with the die-casting machine and attached to the back side of the ejector die assembly by a lost motion connection. In this die assembly, when the machine is in the closed position, the die members of the ejector die assembly, including the angularly movable die core elements, register in the die-closed position to define a cavity therebetween, and in this position, the back-up plate means is held against the rear side of the ejector die assembly and against the rear sides of the angularly movable die core elements by the closing mechanism of the die-casting machine. The integrity of the cavity in the die-closed position is thus maintained. As the die is opened by the die-casting machine, the back-up plate means is withdrawn from the ejector die assembly to the limit of the lost motion connection, and the movable die core elements are retracted. Further withdrawal of the back-up plate means by the die-casting machine moves the ejector die assembly to the full die-open position.
U.S. Pat. No. 5,868,241 discloses an alleged improvement on the V-block die of U.S. Pat. No. 4,206,799 to provide cast V-blocks with closer tolerances. The die disclosed in U.S. Pat. No. 5,865,241 differs from the die disclosed in U.S. Pat. No. 4,206,799 by the addition of complementary male and female surface on the back-up plate (referred to as xe2x80x9cthe ejection boxxe2x80x9d) and the ejector die assembly (referred to as xe2x80x9cthe ejector holder blockxe2x80x9d) to more precisely locate the ejector die assembly (the ejector holder block) with respect to the back-up plate (ejection box) when the two parts are moved into abutment by the die-casting machine, and by the addition of an actuator, in addition to die-casting machine actuator, for moving the back-up plate (ejection box) and the ejector die assembly (the ejector holder block) into abutment.
Thus, recent developments of dies for die-casting V-blocks for internal combustion engines have included a first movable die element (referred to above as an xe2x80x9cejector die assemblyxe2x80x9d and an xe2x80x9cejector holder blockxe2x80x9d), which is carried by the slides and tie bars of the die-casting machine, and which carries the cylinder-forming die core elements reciprocatably, between their extended cavity-forming positions and their retracted part-ejection positions, along axes lying at acute angles with respect to the direction of the die closing and opening movement of the die-casting machine, and a plurality of cavity-forming slides and their hydraulic cylinder actuators. Such recent dies have also included a second movable part connected to the movable platen of the die-casting machine (referred to above as a back-up plate and an ejection block), which is also carried by the slides and tie bars of the die-casting machine separately from the first movable die element to provide a gap between it and the first movable die element for access to the cylinder-forming die core pieces and to provide forward surfaces to abut the cylinder-forming die core pieces in their extended cavity-forming positions to hold, with the closing mechanism of the die-casting machine, the cylinder-forming die core pieces in their extended cylinder-forming positions against the high pressures that are imposed by the injection pressure of the molten metal. Such dies include not only the movable die elements described above, but also a stationary die element (frequently referred to as the xe2x80x9cdie coverxe2x80x9d). Such dies are expensive and frequently too massive and heavy for use with many smaller capacity die-casting machines.
Accordingly, a less expensive and less massive die for die-casting V-blocks for internal combustion engines is needed and will be advantageous.
The invention provides an inexpensive die for die-casting a V-block for an internal combustion engine, which may be operated by a wide range of die-casting machines, including those with inadequate capacity to operate heavy dies for large cast parts. Dies of the invention include, in addition to a stationary die element for the stationary platen of a die-casting machine, only a single movable die element carried by the tie bars and slides of a die-casting machine, carrying the cylinder-forming die core pieces, means for locking the die core pieces in their extended cylinder-forming positions, and the plurality of cavity-forming slides.
The invention provides a die for forming a die cavity for casting a V-block for an internal combustion engine, comprising, in addition to a stationary die element for mounting on the stationary platen of a die-casting machine, a movable die element for mounting on the movable platen of a die-casting machine for movement into cavity-forming engagement with the stationary die element, said movable die element including a cavity-forming surface portion, and carrying a plurality of slides including cavity-forming surfaces for movement transversely with respect to the movement of the movable platen, a plurality of cylinder-forming die core pieces reciprocatable at acute angles in said movable die element between extended positions in the die cavity and retracted positions substantially within said movable die element, and die core locking means, carried by the movable die element, between a first position engaging and locking the die core pieces in their extended cavity-forming positions and a second position free of contact with the die core pieces. The die core locking means preferably comprises a die core locking member having forward die core engaging portions and reciprocatable within the movable die element between a first forward position where its forward die core engaging portions engage rear portions of the die core pieces in their extended positions and a second rearward position out of contact with the die core pieces, and a pair of locks carried by the movable die element for movement transversely of the movement of the die core locking member between first positions between the die core locking member and an internal surface of the movable die element, thereby locking the die core pieces in their extended positions and second positions free of engagement with the die core locking member.